x÷0.7=0.7
x=0.7×0.7
x=4.9
2x-5.7=9.6
2x=9.6+5.7
2x=15.3
x=7.65
(x-0.7)×0.8=2.8
x-0.7=3.5
x=3.5+0.7
x=4.2